1. Field of the Invention
The present invention relates to a repeat type time switch. More particularly, it relates to an improvement of change-over pawls.
2. Description of the Prior Arts
A typical repeat type time switch is shown in FIG. 1 wherein a scale plate (1) is rotated at a constant velocity and a plurality of change-over pawls (2) are independently fitted to the peripheral part of the scale plate and a lever (3) is moved to the arrow line direction by the rising pawl whereby a switch is turned on or off at the raised position of the lever (3) shown by the dashed line.
The change-over pawl (2) can be selectively positioned at two positions. That is, when the pawl (2) is raised as shown in FIG. 3, the tooth (2a) is fitted to the lever (3) whereas when the pawl (2) is fallen as shown FIG. 4, the tooth (2a) is detached from the lever (3).
The positioning of the pawl at the two positions is attained by the resilience of the pawl and the friction resulted between the pawl and the contact part such as the scale plate (5), a guide (6) and a tension plate (7).
Rectangular holes (5a) in which each pawl is inserted are formed on the scale plate (5) for the number of the pawls each with an equal gap. The guide (6) can be a groove (6a) for preventing the movement of the pawl (2) to the tangential direction with the regulation of the rectangular holes (5a) on the scale plate. The grooves (6a) are formed for the number of the pawls each with an equal gap. The tension plate (7) is to prevent the falling of the pawl (2) and a rivet (8) is to fix the contacted parts into one piece.
In said structure, when the change-over pawl (2) corresponding to a desired time is raised at the upper position, the switch (4) can be turned on and off for the time proportional to the number of the raised pawls (2) from such time.
However, the conventional time switch having said structure, has been prepared as follows. As shown in FIG. 4, the independent change-over pawls (2) are respectively inserted into the rectangular holes (5a) on the scale plate and the groove (6a) of the guide and the pawls are pressed by the tension plate (7) and are fixed by caulking the tension plate by the rivet (8).
Therefore, the following disadvantages are found.
(1) Each pawl is prepared by press-stamping whereby a long operation time is required for the preparation of the parts and a uniformity of the quality of the parts are not easily attained and a large loss of the substance is found (loss of the substance in the preparation of the parts).
(2) Each small pawl is fitted to the scale plate whereby a long time for assembling is needed and an automatic operation for the assembling is not easy.
(3) Tack assembled change-over pawls are easily detached before caulking for fixing. Accordingly, special care is needed in the assembling.
(4) A fault of the assembling in failure or error is easily caused.
(5) The parts are relatively small and a large number of the parts is assembled whereby the control for the parts are not easy (in the conventional one 96 parts are assembled).